The traditional form of detergent compositions for use in automatic dishwashing or laundry machines is granular or particulate. Such compositions are measured and dosed by the consumer and placed in the dispenser of the machine which is located in the door in the case of dishwashing machines or the dispensing tray of an automatic laundry washing machine.
In order to simplify the dosing of detergents for automatic washing machines however, many of the automatic washing detergent compositions are now provided in the form of non particulate solids such as bars or tablets or briquettes. This provides a number of advantages to both the consumer and manufacturer. Firstly, such tablets prevent spillage of the detergent composition. Secondly, the tablets eliminate the need for the consumer to estimate the dosage of detergent composition required and ensure that the correct dosage of detergent composition per wash is used by the consumer. Thirdly, the use of tablets minimises the contact by the consumer with the composition.
However, there are a number of problems associated with the use of tablets. In order to provide optimum performance benefits the tablets require a certain dissolution profile during the programme cycle of the machine.
In addition, it is also highly desirable that the tablets possess a certain degree of hardness or tablet strength. In particular the tablets should be sufficiently hard to meet safety requirements. Tabletted detergent compositions are typically highly alkaline and thus oral consumption must be avoided. However, tablets often appear attractive to children, who may attempt to consume them.
Furthermore, it is also desirable that the tablets should be hard enough so that they preferably do not deteriorate, lose their structure or decompose upon packing, transport or storage.
Background Art
Detergent tablets and methods of their preparation are known in the art. For example WO 94/23011 discloses stable, bifunctional phosphate-, metasilicate- and polymer free, low alkaline cleaning agent tablet for dishwashing machines. The composition may comprise from 1-60% anhydrous sodium carbonate, 0-60% sodium disilicate and 3-10% water.
WO 93/00419 discloses a process for producing phosphate and metasilicate free, low alkaline cleaning agent tablets for machine dishwashing. The tablets consist of solid alkali salts of at least one polymer of acrylic acid and builders including anhydrous sodium carbonate. The tablets may comprise anhydrous sodium disilicate. The carbonate undergoes mixing alone or together with other builders and the polymer and with from 5-40% water to result in the partial hydration of the carbonate. The remaining components are then added and compressed into tablet form.
WO 91/15568 discloses stable, phosphate free detergent tablets for use in dishwashing machines containing anhydrous meta silicate, nonionics, builders, bleach, 35-60% acrylic polymers, 25-50% anhydrous carbonate, 4-20% anhydrous sodium sulphate and 1-7% water. The tablets are prepared by compression such that they have a flexural strength of at least 120N.
EPO 481 792 discloses detergent compositions in tablet form comprising a persalt, bleach activator and 5-80% detergent builders, polymers (0.5-15%), alkali metal silicates (0.1%-10%), carbonate and sulphate (not disclosed as anhydrous). Water is not disclosed in the description but the exemplified tablet composition comprises 13.5-16.5% moisture in addition to carbonate, alkaline silicate and polymer. The tablets are prepared by compression of the premixed composition.
EPO 170 791 discloses a process for making a washing composition in tablet form. The process consists of granulating bleach activator, nonionic surfactants, quaternary ammonium compounds, fatty amine derivatives and aminopropanionic acid derivatives with tabletting aids and spraying the granulate with a liquid builder and drying to a water content of at most 6% and compressing into tablets.
All of the identified prior art documents disclose means of increasing tablet hardness using compression of the granular detergent composition following pretreatment of the granular composition ingredients. It is thus an aim of the present invention to provide a tabletted detergent composition having increased strength without substantially increasing the compression force.
It is a further aim of the present invention to provide a tablet having increased strength and hardness with minimal adaptation of the compression manufacturing process, particularly with respect to the tooling required for compression of the detergent composition into tablets.
It is a further aim of the present invention to provide a tabletted detergent composition having the desired dissolution profile.